I need to build a large trap door, the trap door 4x5 with frame 6x8 is too small for my model. Other doors/hinges seem to have too much resistance and the door doesn't fall by itself, it must be rotated. Do you have any ideas as to which parts I could use? I thought I could use 3 of these doors together, the problem is finding the right counterpart.
This hinge combined with a technic pin lets you easily make large trap doors. You can see a train-track-sized trap door in this model using two of these parts. In this model the trap door falls down when you retract an axle that normally holds it up. Other arrangements are possible.
The beauty of this particular hinge is that it is symmetrical, so there aren't two different halves to keep track of, and you can use any kind of technic pin you want. The relatively long plate on it makes it sturdier than some of the older variants like this one.
You can build your own trap door from System and Technic pieces. Use plates for the surface and frame (maybre reinforced by bricks if necessary), and attach one or more (depending on the weight and size) Technic joints underneath. I have no pieces with me at the moment, so I can't show you, but if you need clarifications, I'll look up images of the pieces I'd use.